A polar bear in Alaska. Credit: U.S. Fish and Wildlife Service,
Steve Hillebrand

A polar bear at rest. Credit: U.S. Fish and Wildlife Service,
Susanne Miller

UB researcher Charlotte Lindqvist led the study, which is part
of a larger research program devoted to understanding how the polar
bear has adapted to the harsh Arctic environment. Credit:
University at Buffalo, Douglas Levere

BUFFALO, N.Y. — In the winter, brown and black bears go
into hibernation to conserve energy and keep warm.

But things are different for their Arctic relative, the polar
bear. Within this high-latitude species, only pregnant females den
up for the colder months.

So how do the rest survive the extreme Arctic winters?

New research points to one potential answer: genetic adaptations
related to the production of nitric oxide, a compound that cells
use to help convert nutrients from food into energy or heat.

In a new study, a team led by the University at Buffalo reports
that genes controlling nitric oxide production in the polar bear
genome contain genetic differences from comparable genes in brown
and black bears.

“With all the changes in the global climate, it becomes
more relevant to look into what sorts of adaptations exist in
organisms that live in these high-latitude environments,”
said lead researcher Charlotte Lindqvist, PhD, UB assistant
professor of biological sciences.

“This study provides one little window into some of these
adaptations,” she said. “Gene functions that had to do
with nitric oxide production seemed to be more enriched in the
polar bear than in the brown bears and black bears. There were more
unique variants in polar bear genes than in those of the other
species.”

Co-authors include scientists from UB, Penn State University,
the U.S. Geological Survey Alaska Science Center, Durham
University and the University of California, Santa Cruz.

The genetic adaptations the research team saw are important
because of the crucial role that nitric oxide plays in energy
metabolism.

Typically, cells transform nutrients into energy. However, there
is a phenomenon called adaptive or non-shivering thermogenesis,
where the cells will produce heat instead of energy in response to
a particular diet or environmental conditions.

Levels of nitric oxide production may be a key switch triggering
how much heat or energy is produced as cells metabolize nutrients,
or how much of the nutrients is stored as fat, Lindqvist said.

“At high levels, nitric oxide may inhibit energy
production,” said Durham University’s Andreanna Welch,
PhD, first author and a former postdoctoral researcher at UB with
Lindqvist. “At more moderate levels, however, it may be more
of a tinkering, where nitric oxide is involved in determining
whether — and when — energy or heat is
produced.”

The research is part of a larger research program devoted to
understanding how the polar bear has adapted to the harsh Arctic
environment, Lindqvist said.

In 2012, she and colleagues reported sequencing the genomes of
multiple brown bears, black bears and polar bears.

In a paper in the Proceedings
of the National Academy of Sciences, the team said comparative
studies between the DNA of the three species uncovered some
distinctive polar bear traits, such as genetic differences that may
affect the function of proteins involved in the metabolism of fat
— a process that’s very important for insulation.

In the new study, the scientists looked at the mitochondrial and
nuclear genomes of 23 polar bears, three brown bears and a black
bear.

The research was funded by the University at Buffalo and the
National Fish and Wildlife Foundation.